The present invention relates to an improvement over commonly assigned application Ser. No. 97,029, filed Nov. 21, 1979, the disclosure of which is incorporated herein by reference.
For a micellar fluid to be effective in enhanced oil recovery, the salt tolerance of the fluid should closely match the salt concentration of the water used in the process, which is usually constituted by the brine found in the oil reservoir. That is, the optimal salt concentration for the micellar fluid (i.e. the salt concentration of the brine at which the micellar fluid generates the largest amount of microemulsion phase between the displaced oil and brine) should closely match the brine concentration in the reservoir.
The optimal salt concentration for micellar fluids compounded with the current surfactants of choice, i.e. petroleum sulfonates, can be altered to closely match the brine concentrations in various oil reservoirs. However, this involves considerable work to pick an alcohol (cosurfactant) that will with the surfactant produce a fluid of proper optimal salinity. Considerable work may also be involved to pick the appropriate surfactant to alcohol ratio to produce a fluid of proper optimal salinity. All of this adds to the complication of enhanced oil recovery. Equally important, it is often necessary to use expensive alcohols, such as ethoxylated alcohols, hexanol and the like, to achieve the proper optimal salinity. These add greatly to the chemical cost of using such fluids for enhanced oil recovery.
In commonly assigned application Ser. No. 97,029, a new emulsifier system for use in enhanced oil recovery is disclosed. This system comprises a mixture of an alcohol having no more than 12 carbon atoms and a neutralized oxidized solvent extracted oil. No indication is given, however, of how to match the optimal salinity characteristics of these emulsifier systems to the brine encountered in particular oil reservoirs.
Accordingly, it is an object of the present invention to provide a means for adjusting the optimal salinity of emulsifier systems produced in accordance with the aforementioned application Ser. No. 97,029, so that such emulsifier systems can be tailor-made for use with specific petroleum reservoirs.